1 files changed, 62 insertions, 3 deletions

diff --git a/include/block/block.h b/include/block/block.h
index 4de8d8f..25e2996 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -13,7 +13,7 @@
 /* block.c */
 typedef struct BlockDriver BlockDriver;
 typedef struct BdrvChild BdrvChild;
-typedef struct BdrvChildRole BdrvChildRole;
+typedef struct BdrvChildClass BdrvChildClass;
 
 typedef struct BlockDriverInfo {
     /* in bytes, 0 if irrelevant */
@@ -268,6 +268,62 @@ enum {
     DEFAULT_PERM_UNCHANGED      = BLK_PERM_ALL & ~DEFAULT_PERM_PASSTHROUGH,
 };
 
+/*
+ * Flags that parent nodes assign to child nodes to specify what kind of
+ * role(s) they take.
+ *
+ * At least one of DATA, METADATA, FILTERED, or COW must be set for
+ * every child.
+ */
+enum BdrvChildRoleBits {
+    /*
+     * This child stores data.
+     * Any node may have an arbitrary number of such children.
+     */
+    BDRV_CHILD_DATA         = (1 << 0),
+
+    /*
+     * This child stores metadata.
+     * Any node may have an arbitrary number of metadata-storing
+     * children.
+     */
+    BDRV_CHILD_METADATA     = (1 << 1),
+
+    /*
+     * A child that always presents exactly the same visible data as
+     * the parent, e.g. by virtue of the parent forwarding all reads
+     * and writes.
+     * This flag is mutually exclusive with DATA, METADATA, and COW.
+     * Any node may have at most one filtered child at a time.
+     */
+    BDRV_CHILD_FILTERED     = (1 << 2),
+
+    /*
+     * Child from which to read all data that isn’t allocated in the
+     * parent (i.e., the backing child); such data is copied to the
+     * parent through COW (and optionally COR).
+     * This field is mutually exclusive with DATA, METADATA, and
+     * FILTERED.
+     * Any node may have at most one such backing child at a time.
+     */
+    BDRV_CHILD_COW          = (1 << 3),
+
+    /*
+     * The primary child.  For most drivers, this is the child whose
+     * filename applies best to the parent node.
+     * Any node may have at most one primary child at a time.
+     */
+    BDRV_CHILD_PRIMARY      = (1 << 4),
+
+    /* Useful combination of flags */
+    BDRV_CHILD_IMAGE        = BDRV_CHILD_DATA
+                              | BDRV_CHILD_METADATA
+                              | BDRV_CHILD_PRIMARY,
+};
+
+/* Mask of BdrvChildRoleBits values */
+typedef unsigned int BdrvChildRole;
+
 char *bdrv_perm_names(uint64_t perm);
 uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm);
 
@@ -296,7 +352,8 @@ int bdrv_parse_discard_flags(const char *mode, int *flags);
 BdrvChild *bdrv_open_child(const char *filename,
                            QDict *options, const char *bdref_key,
                            BlockDriverState* parent,
-                           const BdrvChildRole *child_role,
+                           const BdrvChildClass *child_class,
+                           BdrvChildRole child_role,
                            bool allow_none, Error **errp);
 BlockDriverState *bdrv_open_blockdev_ref(BlockdevRef *ref, Error **errp);
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
@@ -352,6 +409,7 @@ BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts,
 void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr);
 void bdrv_refresh_limits(BlockDriverState *bs, Error **errp);
 int bdrv_commit(BlockDriverState *bs);
+int bdrv_make_empty(BdrvChild *c, Error **errp);
 int bdrv_change_backing_file(BlockDriverState *bs,
     const char *backing_file, const char *backing_fmt);
 void bdrv_register(BlockDriver *bdrv);
@@ -540,7 +598,8 @@ void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child);
 BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
                              BlockDriverState *child_bs,
                              const char *child_name,
-                             const BdrvChildRole *child_role,
+                             const BdrvChildClass *child_class,
+                             BdrvChildRole child_role,
                              Error **errp);
 
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);